Method of removing hair and wool from animal hides and skins



METHOD QF-REMOVINGHAJR'AND WOOL FROM RIDES-AND SKINS Haskiel Zalcman;Braybrook, Victoria, Australia No-Drawing, ApplicationApi-il1%1951;

Serial=No.= 22-1,11'5.

Genus-priority; ncafibn-Ausannoctwer-rs; 1949 6. Claims. (Cl1..8=--94-.1-6)

This invention relates to the dehai'ring or removal. ofhair or woolfrlom aniinal' skins. us'i'ngthe paintihgprocr ess wherein a paintcomposition is applied to the. flesh. side of theskinso that directcontact with thehair or wo'o'l is avoided'so far as is" practiable.

The inventionis also particularly though not. excliisively concernedwith the removal of wool from sheepskins.

In the known or existing painting processes. for. d ehairing orde-wooliiig skins, it is. customary'toibrush. or spray theflesh side ofthe skin with a Paint? consisting of a .miXture of sodium sulphide(Nazsj-"and/or sodium: hydrosulp'hide (NaHS) and lime (CaO). in, waterin the. desired"concentration with or withoutlaninert filler toproducethe required consistency.

The presence ofv sodium salts in such paints? results in. a relativelyhigh pH value which causes appreciable. damage to the hide substance inthe peltor. skinanc'Lto the Wool or hair. Moreover in addition totheactuah destruction of hide substance caused by the high pH.

value, the reaction between. sodium ions and. hid e asubstance in suchpaints at pH values? above .1010. .results.

in 'plumping or swelling of the pelt or skin which. is.

the cause offurther permanent damage. Plumping also... has an. adverseeffect on depil'ation. because .it con'strictsx the, opening, of thehair. or woolv follicle. so. that. even. though the root is sufiicientlyloosenedit cannot be readily pulledunless the bulk ofthe root is.pulped'by more. drastic chemicaliaction.

For a considerable ti'meithas been generally. recogk nized that wheneversodium sulphide nazs or..sodi-um\ hydrosulphide (N aHS) is used as abasic constituentiha pai'nt,'d'amage to the skins and; where the. is. a.

1 the range o'fabout 28% to about 4% each by weightof' sheepskin to thewool as Well is unavoidable. Wooliso. pulled is.not to becomparedwith-vi'rgin Wool,

fibers becoming h'arshand' reduced in tensile strength and.

elasticity. They are thickened so. that a woolofjfor in:

stance a 58 count is reduced in count toapprbximatelY.

56. The reduction in tensile strengthresults inalower tear intop-makingand the wool is discolored. and. wil1l not dye evenly. As a resultofithisdamage thewooll' is invariably graded into a lower grade thanvirginiwool.

of the same fineness and character.

The. object ofthe present invention isto achieve.satis.-' factorydepilation at av pH so far. below theefiective minimum in the prior artasto reduce damageinlhepelt.

orhair or wool to a negligible quantity. This is achieved: by 1 (a)Eliminating the cause, of. excessive. plumping,.and.. so avoiding theadverse binding effect on. the. hair: on

wool root.

(b) By increasing thehydrosulphiderion concentration and (c) Bycontrolling the pliildown to the minimum value necessary for depilationhaving regard to the depilation load being kept to. at minimumrandthehydrosui'phiderion concentration being; increased: to can. economic:maximum;

These objectives are attained broadly by using a--paihfl= fen-example,.kao'lint.

.2. that: isrsubstantially devoid of' sources "of. monovalent' metalions; and Which: isr maintained; ata pH of less than about L2. The:paint. contains: in addition: to water a source.- of. hydroxyl ions, asource of sulphideor hydrosulphide ions;. and: may contain-a buflfersubstance for controlling or repressing the hydrox-yl' ion concentrationof. the paint, thereby tocontinuously-maintain:thepaint at relatively.low pH? as compared with paints newcommonly used. a

Theseobjecti'ves are attained more specifically, and

' preferably, by'sel'ecting :as the unhairing accelerator calciumhydrosulphide (.Ca(HS )2.). which. by reason ofitspropertyof depressingpI-Iwhile. .not causing any Vplumpe ing beyond that. caused. byihn'e'alone enables the hydro sulphide ion concentrationltor be heavilyincreased;

The paint composition preferably comprises calciumhydrosulphide(-Ca'('HS)2) andfllime (CaO) and water mixed in l proportion, theconcentration of-calcium-hydro' sulphide. .(.Ca( HS-) 2-) being withinthe range of about 2%.-to-about 30%: and the concentration? of lime((CaO) being-.withimthe. range ofabout 33%: to 'about "l'% each by"weight-oft. the: compositioni to' forrn a .paint." of suitableconcentration for. applicationvtoi the: skins; the consistency of the.fpainti being adjusted as necessary by the-addition: of. am inert'filler; The inert filler' may be;

The: inventioni relatesbasically to the method oidewooling; sheepskins-andrdehairing Iski'ns' whichhcomprise's applyingrto the fleshsideofirtheislins a paint cornposi tion compnisingca'lcium.hydrosulphid'e (Ca'(HS)2)' and lime- CaO.) and water'mixedrinsproportiong the; concen proved method iss'a compositionconipris'iiig calcium hy-- drosulphide: (GatHSQa )E.-and:limei:(a0)' andwater mixed in proportion the concentraisiontoti 'eal'cium'hydrosulphid'e (Ca(HS.).2) being within the range of a-bout.-3 to about"l0'%,.and. the concentration o' f' lime (cao being within thecomposition to form a paint of suitable concentration for application tothe skins the consistency of the painti bein g adjusted as necessary bythe a'dditi'on ofan inemefillerii I-t 'will be untle'rstood th'attheihventionalso provides the: method of-jde-woolin'g sheepskins and d'e-,

hai'riirg skin's; as hereinbefore describedbut using the last&

mentioned'composition.

The 'comp'ositionis prepared simply by mixing the calciumrhydrosulphide': '(Ca'( HS'-)2.)[ and jlii'ne'" (-CaO") and?waterriniproportiomwithbr withont the inert filler'as i's necessaryforth'e' adjustment of the consistency of the" compositions, to obtainpaints ofsuitable' concentration for application t'o the' 'sk-iiis; asexplained hereinafter; r

The p'aintfis applied' to the skin by brushing or spraying-i omit) thefl'esli 'side of- 'the latter which is then-left for a predeterminedperiod before the hair or wool is subjected to "the-pulling or otherremoving operation; Generally; the composition isof "such concentration;with relation to the nature of the skin as hereinafter more fullyexplained; that i't achieves its object in accordance with: theinvention, within a b'out 24 hours after application toith'esk'ins.

rm th'er treatment i of skins other than 'sheepsli ins and hides, theperiod of depilation is lengthened a's-neeessary-- Patented Dec; 25 01956 or hide to be treated.

In the prior art it was generally acceptedthat depilation was forpractical purposes impossible at a pH lower than 12.3-12.5 which viewled to the conviction that depilation by painting with a compositioncontaining a high concentration of calcium hydrosulphide (Ca(HS)z) wasquite impossible by reason of the progressive reduction in pH as shownby the following table based on the applicants work- EFFECT OF CALCIUMHYDROSULPHIDE (Ca(HS)2) ON THE pH OF CALCIUM HYDROXIDE (Ca.(OH)2) SUS-PENSIONS But it has been found by experiment by the applicant thatefiective depilation of sheepskins can be achieved by painting with aconcentration of calcium hydrosulphide (Ca(HS)2) as high as 30% byweight of the composition with the resultant pH as low as 9.9. At thisconcentration it was found to be unnecessary to provide more lime (CaO)than 1% by weight of the composition. For economic reasons such a highconcentration of calcium hydrosulphide (Ca(HS)z) can be regarded asextreme and only significant as indicating the lower limits of hydroxylion concentration at which depilation is possible.

Further experiments demonstrated that with a concentration of calciumhydrosulphide (Ca(HS)z), as low as 2% by weight of the composition couldbe used if the proportion of lime (CaO) were increased to 33% by weightof the composition.

The results of the last mentioned experiment indicated that the pH (inthis case 12.07) was higher than the optimum because the wool thoughmuch superior to wool removed by the sodium sulphide process was damagedto some extent.

Within these two extremes it has been found in practice that it ispreferable to observe the following narrow limits according to the kindand type and condition of the skin and particular working conditions.

Calcium hydrosulphide (Ca(HS)z) about 3% to about Lime (CaO) about 28%to about 4%.

The experiments above referred to and the relative proportions ofcalcium hydrosulphide (Ca(HS)2) and lime (CaO) used bring out a numberof factors, the significance of which appear not to have beenappreciated in the prior art. Without a proper appreciation of them itwas almost inevitable that it would be assumed, as was done, thatsatisfactory depilation with high concentrations of calciumhydrosulphide (Ca(HS)z), or equivalent sources of hydrosulphide ions, isimpracticable.

The factors referred to are:

1. That the plumping or swelling of a skin resulting from the presenceof substantial quantities of monovalent cations in the conventionalsources of hydrosulphide anions, that is, sodium sulphide (NazS) andsodium hydrosulphide (NaHS), required a pH value high enough to pulp thebulk of the hair or woolroot, due to the fact that the follicle of theroot was constricted by theplumping action;

2. Thatif a source of hydrosulphide anions associated with polyvalentcations is used a very much lower pH value would loosen the hair or woolroot sufliciently to enable it to be removed since the plumping actionisisubstantially eliminated;

3. That despite the facts that the depressing of the pH value of a limesuspension, as by the presence of calcium ions, is caused by thedepressing of the solubility of the lime (CaO) or other source ofhydroxyl ions, and that hydroxyl ions react by combination with collagenand saponification of fat in a skin thus involving a reduction ofhydroxyl ion concentration available to react on the keratin of the hairor wool root, it is still possible I to bring sufficient additional lime(CaO) or other source of hydroxyl ions into solution to replenish theloss of hydroxyl ion concentration even where the pH of the compositionwhen applied is as low as 9.9. This is to be explained by the followingfurther factors;

4. That the loss of hydroxyl ions due to reaction with collagen and fatvaries with the concentration of the hydroxyl ions at various pH values,and appears to be relatively insignificant at low pH values as comparedwith that at high pH values. This would appear to follow from the factthat the concentration of hydroxyl ions at a pH of 11 is only one-tenthof that at a pH of 12, and onetwentieth of that at a pH of 12.3;

5. That at any given solubility of lime the rate at which undissolvedcalcium hydroxide (Ca(OH)2) in a composition can be brought intosolution, can be increased by increasing its bulk, and, therefore, thesurface of it exposed to solution.

Having regard to the last two foregoing factors, it has been found thata proportion of 1% lime (CaO) provides a sufficient surface ofundissolved or unhydrolized hydroxide (Ca(OH)2) to provide the necessaryreplenishment of hydroxyl ions at a pH of 9.9, and that at a pH of 12.15a considerably larger proportion of lime (CaO) is required.

solution. Each of these factors must be taken into account according tothe anticipated loss of hydroxyl ions. If the skin to be treated is athick and/or fatty skin increasing the surface of undissolved calciumhydroxide (Ca(OH)2) exposed to solution may not be suflicient withoutreducing the proportion of calcium hydrosulphide (Ca(HS)2) so as toreduce the depressing effect of the calcium ion concentration on therate of solubility. Experience has led the applicant to believe that itis desirable in some instances to limit the proportion of lime "(CaO)and therefore the surface of lime (CaO) exposed to solution to thatwhich is no more than suflicient to overtake towards the end of theselected period of skin treatment, the loss of hydroxyl ions due toreaction. If the proportion of lime (CaO) is not so limited depilationwill still be achieved but both the skin and the Wool will sufier somedamage indicating that the hydroxyl ion concentration at its fullstrength reacts for too long a period on the skin and wool roots. Hencethe desirability, if the best results are to be secured where adjustmentof consistency of a paint is called for, for the addition of anPRACTICAL EXAMPLES OF TREATMENT Example 1 A sheepskin with a wool countof 58 after being washed, soaked and deburred was painted with a paincon- About 7% calcium hydrosulphide (Ca(HS)z) About 14% lime (CaO) About6% kaolin About 73% water.

' After painting the skin was folded in the middle and hung over awooden pole for a period of 24 hours. The wool was then removed from theskin. Upon inspection it was found that the wool had a quality superiorto that obtainable by treating a similar skin according to the practiceshitherto followed in the art, whilst the skin likewise was in a superiorcondition.

The skin treated in the above example was of average condition, i. e.,characterized by that'degree of thickness and fat content associatedwith the skin of a sheep grown under average conditions as to rainfallin a locality suitable for the growing of wool of 58 count. The skin ofa sheep grown under drought conditions, is less thick and carries lessfat than the average and conversely a sheep grown under conditions ofheavy rainfall and overabundant feed is thicker and carries more fatthan the average.

Sheepskins vary as to thickness and fat content according to typeas-well as condition and for a similar reason. Classified as to typeaccording to the count of wool they carry skins carrying wool of highercounts are less thick and fatty than skins carrying wool of lower countsfor the reason that fine wools are grown in drier areas than are coarsewools. But this variation is not very material in the case of skinscarrying Wool of counts above 58 first because the variation isrelatively slight and next because it is offset by the occurrence offolds in the skins of sheep carrying fine wools or what is described asa ribby condition in its skin. I

The composition used in the above example was found by trial to be thatmost suited to the treatment of skins of the type (expressed in terms ofwool count) of a 56-58 count and of average condition. Taking thiscomposition as a norm the operator should increase the proportion ofcalcium hydrosulphide (Ca(HS)2) and decrease that oflime (CaO) Where theskins have the characteristic of a lesser thickness and fat content thana skin of 56-58 wool count of average condition whether thatcharacteristic is due to variation in type or condition or both.Conversely, where the skins to be treated are characterized by greaterthickness and fat content the operator should decrease the proportionof- -calcium hydrosulphide and increase that of lime.

Example 2 As an illustration of adjustments which shouldbe made, theexample of a sheepskin of average condition and havinga wool count of 50may be quoted. A skin of this type and condition after being washed,soaked and deburred was painted with a paint containing About 3% calciumhydrosulphide (Ca(HS)2) About 25% lime (CaO) About71% water.

After. painting the skin was folded in the middle and hung over a woodenpole for a period of 24 hours. The wool was then removed from the skin.As in the case of the previous example it was found on inspection thatboth the 'wool and the skin were of superior quality and condition type'may beitreated in-the same manner-as skins of the type of a wool countof 56-58 with 'similarvari'ations according to condition.

With every skin of whatever type or condition it is necessary to apply apaint of lower calcium hydrosulphide (Ca(HS)2) concentration and higherlime (CaO) concentration to theneck and butt portions of the skin wherethe skin is thicker than it is elsewhere. As an indication of theadjustment here called for it may be taken that where a paint as inExample 1 above is suitable for the main part of the skin a paint as inExample 2 would be used on the neck and butt.

The proportions in all the above examples are adjusted to a period ofdepilation of about 24 hours at normal room temperature, say 70 or F.This period is normal practice in the fellmongering art'and thetfactthat it is so, operates very much to the disadvantage of'the usersof paints hitherto used in the art. Operating at a high pH, as has beenso in the past, it is impossible to I leave skins painted over a weekendwithout seriously increasing the damage to both skin and wool. Thisfurther damage is either accepted or the wool is pulled during theweekend at increased labor cost. By the practice of this invention skinsmay be left over a weekend before pulling without serious increase indamage to either the skin or wool.

The treatment of hides and skins other than sheepskins follows the sameprinciples, but the period of depilation varies from 24 hours to 96hours or even longer according to the thickness type and condition ofthe skin or hide to be treated.

A salted calfskin of approximate. weight 5 lbs. green Was washed andsoaked for about 12 hours and then fleshed and painted with a paintcontaining,

About 5% calcium hydrosulphide (Ca(I-IS)2) About 7% lime (CaO) About 88%water.

After painting the skin Was folded in the middle and laid on a barrowfor a period of 24 hours.

The skin was then dehaired in a skudding machine and it was found thatthe hair was in a good condition and the skin Was in good condition.

The best results are achieved particularly with sheepskins characterizedby thickness and excessive fat by previous soaking and the action ofmachine deburring also contributes to more effective depilation at aminimum pH. Though soaking of the skin is not essential it is fotmd thatafter soaking the'proportion of (Ca(HS)2) may be increased and the pH ofthe composition consequentially decreased beyond what is necessary wherethere is no previous soaking.

Although calcium hydrosulphide and lime in the proportions indicatedhave been found highly satisfactory in practice, there are othersubstances and modifications of the process that may be used to obtainthe desired results. The first requirement is that the paint bedevoid,or substantially devoid, of sources of monovalent metal ions, and thisis true whether calcium hydrosulphide is used, or some equivalentsubstance. The substantial elimination of the sources of monovalentmetal ions substantially avoids plumping or swelling of the skin, andthereby makes possible the use of lower pH solutions for the depilationof the wool or hair. This concept itself is of great importance in thepractice of the invention.

Broadly speaking, the invention contemplates a composition substantiallydevoid of sources of monovalent metal ions, and comprising any suitablepolyvalent metal source of hydroxyl ions, as hereinafter defined asuitable source of sulphide or hydrosulphide ions, and, where nec-'essary, a bufier material for controlling the hydroxyl ion concentrationin the composition, so that the composition has a pH value of about 12or less. Although lime is obviously the most practical source ofhydroxyl ions, other suitable bases such for example as barium hydroxide (Ba(OH)2) or strontium hydroxide (Sr(OH)2) might" 7 also beused, andpossibly also magnesium hydroxide )2)- The hydrosulphide ion which mustbe present in suitable quantities to eifect depilation may be providedin various ways. The most effective source is calcium hydrosulphidewhich should be in the proportion of 2 to in order to maintain the pH ofthe solution below about 12.

Instead of mixing calcium hydrosulphide with lime, the hydrosulphideions may be provided by passing hydrogen sulphide @S) into a slurry oflime in water, thereby forming a mixture of calcium hydrosulphide andunchanged lime. Or, the hydrogen sulphide could be passed into a slurryof lime and calcium sulphide, in which case the hydrogen sulphide wouldbe absorbed and the pH of the solution lowered.

Instead of using a calcium salt as a base for the hydrosulphide ion,other metal sulphides may be used so long as the metal is not monovalentand the metal sulphide is appreciablysoluble in lime water, or, if notsoluble, then if the hydroxide of that metal is even more insoluble inwater, so that the metal sulphide will act with calcium hydroxide toform calcium sulphide or hydrosulphide and an insoluble metal hydroxide.

Accordingly, sulphides of barium, strontium, magnesium, and aluminum maybe used satisfactorily, although in some instances of high solubility abuffer material would have to be used in order to control the pH tobelow about 12, such bufier being a suitable acid or soluble calciumsalt.

Calcium chloride or a soluble calcium salt may be used as a control byproviding calcium ions which repress the solubility of the calciumhydroxide to thereby maintain the desired pH value of about 12 or less.

Instead of using a soluble calcium salt a suitable acid may be usedprovided such acid produces a calcium salt that is at least moderatelysoluble. Thus, hydrochloric acid, acetic acid, hydrobromic acid, formicacid, lactic acid, nitric acid, nitrous acid, tartaric acid, and citricacid, are common acids whose calcium salts are soluble, and whichwouldnormally provide the soluble calcium salt needed to repress thesolubility of calcium hydroxide.

Even some sulphides that would normally be deemed ineffective in a limesolution, because they form insoluble sulphides, may be made effectiveif used with some added substance that would cause them to dissolve. Allthat appears to be necessary is that the-sources of monovalent cationsare substantially avoided, that there be a suitable source of hydroxyland hydrosulphide ions, and that the pH is properlycontrolled by buttersubstances when necessary to a value of about 12 or less.

In this specification and the following claims the word paint hasthemeaningunderstood by those skilled in the art of de-Wooling sheepskinsand dehairing skins; the

lime .(CaO') found to achieve depilation within agiven period with themost favorable results as regards the skins and in the case ofsheepskins the wool as well having regard'to the thickness and fatcontent of the skins; and, the expression inert filler means a finelydivided substance the primary purpose of which'as an additive to thecomposition is to thicken the'consistency of the composition.

While I have described particular embodiments of my invention, it willoccur to those skilled in the art that various changes, modificationsand equivalents may be made or used without departing from my invention,and I, therefore, intend, in the appended claims, to cover all suchchanges, modifications and equivalents as fall within the true spiritand scope of my invention.

This application isa-continua-tiou in part of-my earlierapplication-Serial No. 180,897, filed August 22, 1950, now abandoned;

I claim:

1. In the art of depilating lamb and sheep skins by applying adepilatory paint to the flesh side of the skins, the method of effectingdepilation to obtain high quality wool while preserving the quality ofthe skin which consists in applying to the flesh side of the skin anaqueous composition which is substantially free of sources of monovalentmetal cations and which comprises calcium hydrosulphide and lime, thecalcium hydrosulphide being about 3 to 7% and the lime about 25 to 14%,each by weight of the composition, the proportion of calciumhydrosulphide decreasing and of lime increasing within the above rangeswith the increasing thickness and fat content of the skin, thecomposition having a pH of not more than 12 and not less than about11.7, and the source of hydroxyl ions being suflicient in quantity toprovide an undissolved reserve thereof suspended in the composition;allowing the composition to remain on the skin until the wool isloosened, and then pulling the loosened wool from the skin.

2. In the art of depilating lamb and sheep skins by applying adepilatory paint to the flesh side of the skins, the method of effectingdepilation to obtain high quality wool While preserving the quality ofthe skin which consists in applying to the flesh side of the skin anaqueous composition which is substantially free of sources of monovalentmetal cations and which comprises calcium hydrosulphide and lime, thecalcium hydrosulphide being about 3 to 7% and the lime about 25 to 14%,each by weight of the composition, the calcium hydrosulphide decreasingtoward 3% and the lime increasing toward 25% to provide a lower ratio ofcalcium hydrosulphide to lime when the composition is applied to theneck and butt portions of the skin as compared with the ratio of calciumhydrosulphideand lime in the composition applied to other portions ofthe skin, whereby the proportion of calcium hydrosulphide decreases andof lime increases with the increasing thickness and fat content of theskin, the composition having a pH of not more than 12 and not lessthanabout 11.7,-and the-source of hydroxyl ions being sufficient inquantity to provide an undissolved reserve thereof suspended in thecomposition; and allowing the composition to remain on the skin untilthe wool is loosened.

3. In the art of depilating lamb and sheep skins by applying adepilatory paint to the flesh side of the skins, the method of effectingdepilation to obtain high quality wool while preserving the quality ofthe skin which consists in applying to the flesh side of the skin anaqueous composition which is substantially free of sources of monovalentmetal cations and which comprises calcium hydrosulphide and lime, thecalcium hydrosulphide being about 3 to 10% and the lime about 28to 4%,each by weight of the composition, the proportion of calciumhydrosulphide decreasing and of lime increasing within the above rangeswith the increasing thickness and fat content of the skin, compositionhaving a pH of not more than 12 and not less than about 11.6, and thesource of hydroxyl ions being sufiicient in quantity to providean-undissolved reserve thereof suspended in the composition; allowingthe composition to remain on the skin until the wool is loosened, andthen pulling the loosened wool from' the skin.

4. In the art of depilating lamb and sheep skins by applying adepilatorypaint to the flesh side of'the'skins,

hydrosulphide and lime, the calcium hydrosulphide being about 3- to10%andthe lime about28 to 4%, each'by weight of the-composition, thecalcium hydrosulphide decreasing toward*3-% and the limeincreasing'toward 28% to provide a lower-ratio of calcium hydrosulphideto'lim'e 9 when the composition is applied to the neck and butt portionsof the skin as compared with the ratio of cal- 1 cium hydrosulphide andlime in the composition applied to other portions of the skin wherebythe proportion of set forth in claim 1 in which the aqueous compositionincludes an inert filler in such quantity as to give the composition theconsistency required for application and adherence to the flesh side ofthe skins.

6. In the art of depilating lamb and sheep skins by applying adepilatory paint to the flesh side of the skins, the method of effectingdepilation to obtain high quality wool while preserving the quality ofthe skin which consists in applying to the flesh side of the skin anaqueous composition which is substantially free of sources of monovalentmetal cations and which comprises calcium hydrosulphide and lime, thecalciumhydrosulphide being about 3% to 30% and the lime about 33% to 4%,each by weight of the composition, with the lime being at least 7% whenthe calcium hydrosulphide concentration is at about 3%, the proportionof calcium hydrosulphide decreasing and of lime increasing within theabove ranges with the increasing thickness and fat content of the skin,the composition having a pH of not more than 12 and not less than about9.9, and the source of hydroxyl ions being suflicient in quantity toprovide an undissolved reserve thereof suspended in the composition;allowing the composition to remain on the skin until the wool isloosened, and then pulling the loosened wool from the skin.

References Cited in the file of this patent UNITED STATES PATENTS Re.4,549 Siebel Sept. 12, 1871 1,041,897 Stone Oct. 22, 1912 2,169,148Jaeger Aug. 8, 1939 2,487,558 Kamlet Nov. 8, 1949 OTHER REFERENCES Thieset al.: article in J. A. L. C. A., vol. 37, 1942, pages 93-102.

Progress in Leather Science 19201945, pages 176, 118 and 189, pub. 1948by Printing Craft Ltd., Mansfield, England.

Moore, in J. A. L. C. A., vol. 22, 1933, pages 206- 216.

Tanning Processes, by Orthmann, publ. 1945 by Hide and Lea. Publ. 00.,pages 1, 2, and 41. (Copy P. O. S. L.)

Progress in Leather Science 1920-1945, page 188, publ. 1948 by PrintingCraft, Mansfield.

Circular to Fellmongers No. 8, 3 p., September 1949, pub. byCommonwealth Scientific & Ind. Res. Or. Div. of Ind. Chem., Melbourne,Australia.

Bowes et 211.: B. L. M. R. A. Lab. Report No. 25, part V, 1946, 8 pages.

1. IN THE ART OF DEPILATING LAMB AND SHEEP SKINS BY APPLYING ADEPILATORY PAINT TO THE FLESH SIDE OF THE SKINS, THE METHOD OF EFFECTINGDEPILATION TO OBTAIN HIGH QUALITY WOOL WHILE PRESERVING THE QUALITY OFTHE SKIN WHICH CONSISTS IN APPLYING TO THE FLESH SIDE OF THE SKIN ANAQUEOUS COMPOSITION WHICH IS SUBSTANTIALLY FREE OF SOURCES OF MONOVALENTMETAL CATIONS AND WHICH COMPRISES CALCIUM HYDROSULPHIDE AND LIME, THECALCIUM HYDROSULPHIDE BEING ABOUT 3 TO 7% AND THE LIME ABOUT 25 TO 14%,EACH BY WEIGHT OF THE COMPOSITION, THE PROPORTION OF CALCIUMHYDROSULPHIDE DECREASING AND OF LIME INCREASING WITHIN THE ABOVE RANGESWITH THE INCREASING THICKNESS AND FAT CONTENT OF THE SKIN, THECOMPOSITION HAVING A PH OF NOT MORE THAN 12 AND NOT LESS THAN ABOUT11.7, AND THE SOURCE OF HYDROXYL IONS BEING SUFFICIENT IN QUANTITY TOPROVIDE AN UNDISSOLVED RESERVE THEREOF SUSPENDED IN THE COMPOSITION;ALLOWING THE COMPOSITION TO REMAIN ON THE SKIN UNTIL THE WOOL ISLOOSENED, AND THEN PULLING THE LOOSENED WOOL FROM THE SKIN.